K2 Builder Alert #4: POSSIBLE BFO RANGE PROBLEM
Wed, 7 Jul 1999

New K2 builders (Serial Numbers 00101 - 00260 ONLY) :

Your humble K2 hardware designers got a little bit too tricky when they substituted MVAM109 varactor diodes for ALL of the MVAM108's in the kit. We trusted Motorola's data sheet, which says that the two have an identical capacitance range.

As it turns out, the MVAM109's don't work as well in our BFO circuit as the 108's (diodes D37 and D38 on the RF board). So, we will be sending all new K2 builders a pair of MVAM108's (or equivalent) to be installed at these two locations. (Field testers already have the 108's.)
 

TESTING THE BFO RANGE

Here's how to tell if you have the BFO range problem:

1. Connect the internal frequency counter probe to TP2 (BFO).
2. Select CAL FCTR in the menu.
3. Hit BAND+ and BAND- and write down your BFO range (you should have already done this on page 56 of your manual).
4. If the BAND- frequency is above 4913.0, it's a good indication that D37 and D38 don't have enough low-end range. We will modify the manual here to make this clear.

Please send your BFO range results to n6kr@elecraft.com for statistical analysis--thanks.
 

WHAT TO DO IN THE MEAN TIME

As I mentioned, we'll be sending replacement diodes.  In the mean time, if your BFO fails the test (above), you may want to operate exclusively on CW REVERSE. In this case the BFO is *above* the crystal filter, where it can easily be positioned.

If you have the BFO problem, you may notice that it's not easy to set up the BFO for CW NORMAL filters--this is because the BFO doesn't go far enough below the center of the filter passband. This will degrade CW normal reception. It will also make LSB on 17m and below and USB on 15m and above sound weak or distorted.

Sorry for the temporary inconvenience. Care packages will go out next week.